Long arc plasma torches are commonly used in plasma chemistry and metallurgy, in plasma costing processes, plasma cutting and welding, and other industrial processes. Plasma torches are also used for vitrification of ceramics and hazardous wastes, in pyrolysis chambers, and in the processing of waste and generation of synthetic fuels. Plasma torches which can generate and deliver a high temperature stream of ionized gas need to meet several difficult requirements. One requirement is longevity of the electrodes, which have a surface region in direct contact with the plasma in a transient point known as the arc attachment. One problem of high energy plasma torches is that the high temperature arc attachment points at the electrode surface are proximal to very high temperatures of the reactive ionized gas, which can corrode the surface of the electrode at the arc attachment point. This surface corrosion subsequently leads to roughness of the electrode surface, which then causes enhanced electric fields in the corroded areas, which then encourages preferential plasma formation in the corroded areas. Another problem inherent in high energy long arc plasma torches is plasma arc initiation. In one prior art device, an external source introduces a plasma into the desired plasma arc extent, after which the ionized gas of the introduced plasma forms a plasma arc across the working electrodes of the plasma torch. In another prior art device, a separate transformer generates one or more areas of localized ionized gas along the path of desired plasma formation between the working electrode, which local plasmas combine upon application of sufficient voltage to the working electrodes. In either device, a separate plasma initiation structure is used at start-up time.
It is desired to provide a long arc plasma torch which self initializes and which provides improved electrode life by ensuring uniform wear of the electrode surface.